| Issue |
90177
|
| Summary |
CTAD: incorrect transformed require-clause for the alias deduction guide
|
| Labels |
clang,
c++20,
clang:frontend
|
| Assignees |
|
| Reporter |
hokein
|
Example:
```
struct Key1 {};
template <class Key>
struct Foo {
Foo(Key);
};
template <class D>
constexpr bool C = sizeof(D);
template <class Key>
requires (C<Key>)
Foo(Key) -> Foo<Key>;
template <class T>
struct HasTemplateParam {
template <class Key>
using Alias = Foo<Key>;
};
class Forward;
struct Test : HasTemplateParam<Forward> {
using Foo1 = decltype(Alias{
Key1(),
});
};
```
clang rejects the above valid code with the following diagnostics:
```
<source>:9:20: error: invalid application of 'sizeof' to an incomplete type 'Forward'
9 | constexpr bool C = sizeof(D);
| ^~~~~~~~~
<source>:12:13: note: in instantiation of variable template specialization 'C<Forward>' requested here
12 | requires (C<Key>)
| ^
<source>:12:13: note: while substituting template arguments into constraint _expression_ here
12 | requires (C<Key>)
| ^~~~~~
<source>:23:25: note: while checking constraint satisfaction for template '<deduction guide for Alias><Forward>' required here
23 | using Foo1 = decltype(Alias{
| ^~~~~
<source>:23:25: note: in instantiation of function template specialization 'HasTemplateParam<Forward>::<deduction guide for Alias><Key1>' requested here
<source>:21:7: note: forward declaration of 'Forward'
21 | class Forward;
```
It seems to be an issue in the transformed require-clause for the alias deduction guide. The require _expression_ should be evaluated on the type `Key1`, rather than the outer type `Forward`.
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